1. Field of the Invention
The present invention relates to an A/V (Audio and/or Video) signal recording/reproducing apparatus for recording a video signal and an audio signal with many channels and a recording method thereof.
2. Description of the Prior Art
Conventionally, an A/V signal composed of an audio signal and a video signal is recorded on a magnetic tape. Such a magnetic tape is referred to as a linear record medium because the A/V signal is linearly recorded on time axis.
Since the magnetic tape is a linear record medium, it takes a long time to edit the A/V signal recorded thereon. For example, as shown in FIG. 4A, when sceans A and B that have been recorded at different positions of a source tape are edited as successive scenes, the scene A is reproduced from the source tape. The scene A is recorded on a destination tape. The scene B is searched and reproduced from the source tape. The scene B is recorded after the position of the scene A on the destination tape. Thus, the scenes A and B are recorded as one A/V signal (see FIG. 4B). In other words, to edit an A/V signal recored on a linear record medium such as a magnetic tape, at least two VCR units are required. In addition, a search time for a signal recorded on the tape is required. The search time is on the order of several seconds to several ten seconds.
To solve such a problem, in recent years, a technique for recording an A/V signal on a non-linear record medium that is randomly accessible has been increasingly used. In this case, as such a non-linear record medium, a hard disk drive is often used.
FIG. 5 is a schematic diagram showing a structure of the hard disk drive. Tracks 101a, 101b, and so forth are concentrically arranged on the record surface of a disk 100 that is a record medium. Each track is divided into sectors 102a, 102b, and so forth each of which has a predetermined data length. In the case of hard disk drives that record signals of computers, the data length of each sector is for example 512 bytes. On the other hand, in the case of hard disk drives that record A/V signals, the data length of each sector is for example 4096 bytes. The tracks 101a, 101b, and so forth are identified by track numbers starting with 0 from the outermost periphery to the innermost periphery. Thus, the tracks 101a, 101b, and so forth with the same numbers are cylindrically arranged on the disk 100. These cylindrical portions are referred to as cylinders. Each cylinder is identified by a cylinder number with the same value as the corresponding track number.
Likewise, sectors 102a, 102b, and so forth of each cylinder are identified by sector numbers starting with 0. When data is read or written, a target track number and a target sector number are designated to a hard disk controller. Thus, a magnetic head disposed at an edge of a movable arm 104 is moved to the target cylinder. This operation is referred to as "seek" operation. The hard disk controller waits until the disk 100 rotates and the target sector comes to the position of the magnetic head 105. This operation is referred to as "rotation wait" operation. Each sector contains a cylinder number, a sector number, and so forth as identification information at the start position thereof. While the rotation wait operation is being performed, the hard disk controller continuously reads the identification information. When the hard disk controller detects the target sector, it starts reading data.
FIGS. 6A and 6B show an edit operation for an A/V signal on the hard disk. As shown in FIG. 6A, scenes A and B are recorded on an outer peripheral track and an inner peripheral track of the hard disk, respectively. When the scenes A and B are edited as one A/V signal, data of the scene A is read and reproduced with a track number and a sector number that represent the position of the scene A. After the data of the scene A has been reproduced, the seek operation and the rotation wait operation are performed with a track number and a sector number that represent the position of the scene B. Thus, the scene B is read and reproduced.
Thus, unlike with a magnetic tape as a linear record medium, on the hard disk as a non-linear record medium, the edit operation for connecting the scenes A and B and for recording the connected scenes on the tape is not performed. In other words, as shown in FIG. 6B, points A.sub.start and A.sub.end that represent the start position and the end position of the scene A and points B.sub.star and B.sub.end that represent the start position and the end position of the scene B are recorded. After data from the point A.sub.start to the point A.sub.end is reproduced, the seek operation and the rotation wait operation are performed. Thereafter, data from the point B.sub.start to the point B.sub.end is reproduced.
In this case, the seek operation and the rotation wait operation performed from the scene A to the scene B take several 10 ms to several 100 ms. This time period is much smaller than that necessary for such operations on the linear record medium. Thus, with such a non-linear record medium, discontinuous data can be continuously reproduced without need to perform the edit operation for connecting scenes. Thus, an A/V signal can be successively reproduced. Consequently, with a non-linear record medium such as a hard disk, the edit operation can be much effectively performed.
Recently, especially in professional field, an audio signal with multiple channels has been increasingly used. For example, an audio signal with four to eight channels has been recorded. For example, an audio signal is recorded in such a manner that a voice sound is recorded on the first channel, other sounds are recorded on the second and third channels, and an effect sound is recorded on the fourth channel.
On the other hand, various audio signals and video signals are recorded in one hard disk drive. Such audio signals and video signals may be edited as one A/V signal. In this case, since the seek operation should be performed for each of audio channels, the number of times of the seek operation and the seek distance increase. Thus, it is difficult to successively reproduce such signals as one A/V signal.
To solve such a problem, conventionally, a technique for recording audio signals and video signals to individual hard disk drives or another technique for recording relevant audio signals and video signals as blocks have been commonly employed.
FIGS. 7A and 7B are schematic diagrams showing a method for recording audio signals and video signals to respective hard disk drives. In this method, as shown in FIG. 7A, only video signals are recorded to a hard disk drive A. On the other hand, audio signals with four channels (first to fourth channels) are recorded to a hard disk drive B.
In this method, when audio signals and video signals are independently edited, as shown in FIG. 7B, these signals can be accessed in parallel. The reproduced A/V signals are temporarily stored in a buffer memory and read therefrom at a proper timing. Thus, they are reproduced as linear A/V signals. Consequently, according to this method, successive A/V signals can be effectively reproduced. However, in this method, since two hard disk drives are required, the cost of the apparatus adversely increases.
FIGS. 8A and 8B are schematic diagrams showing a method for recording relevant audio signals and video signals as blocks. In this method, as shown in FIG. 8A, when a video signal is associated with an audio signal with four channels (first to fourth channels), these signals are recorded as a block.
According to this method, as shown in FIG. 8B, the edit point of the audio signal is the same as the edit point of the video signal. When blocks of audio signals and video signals are edited, the number of times of the seek operation for the hard disk drive is small. Thus, the signals can be effectively edited. In addition, when A/V signals are simply reproduced in succession, the reproduction speed increases.
However, in the case that the edit point of an audio signal is different from the edit point of a video signal, when these signals should be independently edited, as shown in FIG. 8C, as the number of times of the seek operation increases, A/V signals read from the hard disk drive become discontinuous. Thus, it becomes difficult to read the signals from the buffer memory. Consequently, the A/V signals cannot be reproduced in succession.
Thus far, an A/V signal recording/reproducing apparatus that has the advantages of the above-described two methods that allow the parallel reproductions of audio signals and video signals using two hard disk drives and high speed successive reproductions of which relevant audio signals and video signals are recorded as blocks and that is accomplished at low cost has not be developed.